BIRDS. 227 



of the muscles, a number extending down the leg from the 

 pelvis to the outside of the knee, then winding around and 

 blending with the principal muscles of the toes. When 

 the bird settles in roosting, the leg is bent upon the thigh, 

 the weight of the bird acting as a lever that tautens the 

 muscles and draws the toes and claws tightly about the 

 limb or roost ; thus the bird can sleep while standing upon 

 one leg without fear of falling, being held fast by the 

 weight of its body. The tail or caudal vertebrae are mov- 

 able to some extent and end in the plowshare-bone, /, 

 that supports the large quill-feathers of the tail. On the 

 under portion of the skeleton we note the sternum, , or 

 breast-bone, to which the wing-moving muscles are at- 

 tached. In the flying birds, as Fig. 268, it is keeled and 

 has a sharp edge, thus offering a greater surface of attach- 

 ment, but in birds like the ostrich the keel is absent. 

 Above the sternum are the ribs, that vary in number from 

 seven to eleven pairs. In front of the sternum the clavicles 

 join and form a V-shaped bone called the lucky or collar 

 bone (Fig. 268, m). The coracoid bone over which the 

 tendon works to pull up the wing, is seen at e, and this 

 and the scapula and clavicle constitute the " pectoral arch " 

 to which the humerus, a, or first bone of the wing, is at- 

 tached. The position of the elbow is seen at e ; then fol- 

 lows the fore-arm (ulna and radius), fa. The position of 

 the wrist is shown at w ; then follow the carpal and meta- 

 carpal bones, which are joined at the extremities. At the 

 upper end of the metacarpal bones there is a rudimentary 

 thumb (Fig. 268, /). It has a single joint and supports 

 what is called the false wing. The end of the wing (Fig. 

 268, ha) corresponds to the hand, and three rudimentary 

 fingers are generally observed, that correspond to the first 

 and third fingers of the human hand. The fingers only in 

 rare cases are clawed, and" the arm, that in other animals is 

 used for digging, clinging, or crawling, is now only used to 

 propel the bird through the air or water as the case may be. 



